U.S. patent number 8,248,897 [Application Number 12/899,101] was granted by the patent office on 2012-08-21 for method for manufacturing thermally-assisted magnetic recording head comprising light source unit and slider.
This patent grant is currently assigned to Headway Technologies, Inc., TDK Corporation. Invention is credited to Ryuji Fujii, Takashi Honda, Yasuhiro Ito, Nobuyuki Mori, Yoshitaka Sasaki, Koji Shimazawa, Osamu Shindo, Seiichi Takayama, Kosuke Tanaka, Yoshihiro Tsuchiya.
United States Patent |
8,248,897 |
Shimazawa , et al. |
August 21, 2012 |
Method for manufacturing thermally-assisted magnetic recording head
comprising light source unit and slider
Abstract
A method for manufacturing a thermally-assisted magnetic
recording head is provided, in which a light source unit including
a light source and a slider including an optical system are bonded.
A unit substrate is made of a material transmitting light having a
predetermined wavelength, and a unit adhesion material layer that
contains Sn, Sn alloy, Pb alloy or Bi alloy is formed on the light
source unit and/or the slider. The manufacturing method includes:
aligning the light source unit and the slider in such a way that a
light from the light source can enter the optical system and the
unit adhesion material layer is sandwiched therebetween; and
causing a light including the predetermined wavelength to enter the
unit substrate to melt the unit adhesion material layer. The unit
adhesion material layer melted by the light including the
predetermined wavelength can ensure high alignment accuracy as well
as higher bonding strength and less change with time.
Inventors: |
Shimazawa; Koji (Tokyo,
JP), Tsuchiya; Yoshihiro (Tokyo, JP),
Takayama; Seiichi (Tokyo, JP), Mori; Nobuyuki
(Tokyo, JP), Ito; Yasuhiro (Tokyo, JP),
Tanaka; Kosuke (Tokyo, JP), Shindo; Osamu (Tokyo,
JP), Fujii; Ryuji (Hong Kong, CN), Honda;
Takashi (Hong Kong, CN), Sasaki; Yoshitaka
(Milpitas, CA) |
Assignee: |
TDK Corporation (Tokyo,
JP)
Headway Technologies, Inc. (Milpitas, CA)
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Family
ID: |
44647174 |
Appl.
No.: |
12/899,101 |
Filed: |
October 6, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110228650 A1 |
Sep 22, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12726981 |
Mar 18, 2010 |
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Current U.S.
Class: |
369/13.33;
369/112.27; 360/59 |
Current CPC
Class: |
G11B
5/6088 (20130101); G11B 5/314 (20130101); G11B
2005/0021 (20130101); G11B 2005/001 (20130101) |
Current International
Class: |
G11B
11/00 (20060101) |
Field of
Search: |
;369/13.33,13.32,13.24,13.14,13.03,13.02,13.12,112.27,112.29,13.35
;360/59,313,125.31,125.74 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-2009-301597 |
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Dec 2009 |
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JP |
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Other References
Oct. 17, 2011 Office Action issued in U.S. Appl. No. 12/728,510.
cited by other .
U.S. Appl. No. 12/728,510, filed Mar. 22, 2010 in the name of
Shimazawa et al. cited by other .
U.S. Appl. No. 12/628,761, filed Dec. 1, 2009 in the name of
Shimazawa et al. cited by other .
Mar. 6, 2012 Office Action issued in U.S. Appl. No. 12/726,981.
cited by other .
Rottmayer, Robert et al., "Heat-Assisted Magnetic Recording," IEEE
Transactions on Magnetics, Oct. 2, 2006, pp. 2417-2421, vol.
42--No. 10. cited by other.
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Primary Examiner: Neyzari; Ali
Attorney, Agent or Firm: Oliff & Berridge, PLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part application of U.S.
application Ser. No. 12/726,981, filed on Mar. 18, 2010, now
pending.
Claims
The invention claimed is:
1. A method for manufacturing a thermally-assisted magnetic
recording head in which a light source unit including a light
source provided in a unit substrate and a slider including an
optical system provided in a slider substrate are joined with each
other, wherein the unit substrate is made of a material
transmitting light having a predetermined wavelength and a unit
adhesion material layer is formed on a surface of one or each of
the light source unit and the slider, the unit adhesion material
layer containing a material selected from a group consisting of
tin, tin alloy, lead alloy and bismuth alloy, the manufacturing
method comprising the steps of: aligning the light source unit and
the slider with each other in such a way that a light generated
from the light source can enter the optical system and the unit
adhesion material layer is sandwiched between the light source unit
and the slider; causing a light including the predetermined
wavelength to enter the unit substrate to melt the unit adhesion
material layer; and bonding the light source unit and the slider
with each other.
2. The manufacturing method as claimed in claim 1, wherein the unit
adhesion material layer contains a material selected from a group
consisting of Sn, SnAu, SnCu, SnAl, SnSi, SnGe, SnMg, SnPb, SnAg,
SnZn, SnBi, SnNi, SnPt, PbAu, PbMg, PbBi and BiAu.
3. The manufacturing method as claimed in claim 1, wherein the unit
adhesion material layer is made of a material having a melting
point lower than a melting point of a light-source adhesion
material layer used for joining the light source to an electrode
provided on the unit substrate.
4. The manufacturing method as claimed in claim 3, wherein the unit
adhesion material layer is made of a material having a melting
point lower, by 30.degree. C. or more, than a melting point of a
light-source adhesion material layer used for joining the light
source to an electrode provided on the unit substrate.
5. The manufacturing method as claimed in claim 1, wherein a
reflective layer is provided on a surface of the unit substrate
opposed to the slider substrate when joined to the slider, the
reflective layer reflecting the light including the predetermined
wavelength.
6. The manufacturing method as claimed in claim 1, wherein the
light source is activated, and the light source unit and the slider
are aligned in such a way that the light generated from the light
source enters the optical system.
7. The manufacturing method as claimed in claim 6, wherein the
melting of the unit adhesion material layer by the entering of the
light including the predetermined wavelength is assisted by heating
the unit adhesion material layer to a high temperature with a heat
generated from the activated light source.
8. The manufacturing method as claimed in claim 6, wherein the unit
adhesion material layer is repeatedly melted by causing the lights
including the predetermined wavelength to enter the unit substrate
from different directions, to correct variations in relative
positions of the light source unit and the slider caused by the
melting of the unit adhesion material layer.
9. The manufacturing method as claimed in claim 8, wherein the
amount of displacement of the light source unit and the slider with
respect to each other is obtained beforehand in the case that the
unit adhesion material layer is irradiated with a predetermined one
shot of each of the lights from different directions, then the
number of shots of each of the lights from different directions is
determined.
10. The manufacturing method as claimed in claim 1, wherein the
slider comprises a magnetic head element configured to write and/or
read data, and the slider substrate is made of a material having a
lower thermal conductivity than a material of the unit substrate so
that conduction of a heat generated by the entering of the light
including the predetermined wavelength to the magnetic head element
is limited.
11. The manufacturing method as claimed in claim 10, wherein,
during the alignment, a holding means to hold the light source unit
is used as a heatsink for the heat generated by the entering of the
light including the predetermined wavelength.
12. The manufacturing method as claimed in claim 1, wherein the
unit substrate is made of a material selected from a group
consisting of Si, GaAs and SiC, and a YAG laser light is used as
the light including the predetermined wavelength.
13. The manufacturing method as claimed in claim 1, wherein a
circularly- or elliptically-polarized light is used as the light
including the predetermined wavelength.
14. The manufacturing method as claimed in claim 1, wherein a
P-polarized light is used as the light including the predetermined
wavelength.
15. A thermally-assisted magnetic recording head comprising: a
light source unit comprising: a unit substrate made of a material
transmitting light having a predetermined wavelength; and a light
source provided in a source-installation surface of the unit
substrate; and a slider comprising: a slider substrate made of a
material having a lower thermal conductivity than a material of the
unit substrate; a magnetic head element configured to write and/or
read data and provided in an element-integration surface of the
slider substrate; and an optical system configured to propagate a
light from the light source toward a magnetic recording medium and
provided in the element-integration surface, the light source unit
and the slider being bonded by a unit adhesion material layer
melted and solidified with a light that includes the predetermined
wavelength and has passed through the unit substrate, and the unit
adhesion material layer containing a material selected from a group
consisting of tin, tin alloy, lead alloy and bismuth alloy.
16. The thermally-assisted magnetic recording head as claimed in
claim 15, wherein the unit adhesion material layer contains a
material selected from a group consisting of Sn, SnAu, SnCu, SnAl,
SnSi, SnGe, SnMg, SnPb, SnAg, SnZn, SnBi, SnNi, SnPt, PbAu, PbMg,
PbBi and BiAu.
17. The thermally-assisted magnetic recording head as claimed in
claim 15, wherein the unit adhesion material layer is made of a
material having a melting point lower than a melting point of a
light-source adhesion material layer that joins the light source to
an electrode provided on the unit substrate.
18. The thermally-assisted magnetic recording head as claimed in
claim 17, wherein the unit adhesion material layer is made of a
material having a melting point lower, by 30.degree. C. or more,
than a melting point of a light-source adhesion material layer that
joins the light source to an electrode provided on the unit
substrate.
19. The thermally-assisted magnetic recording head as claimed in
claim 15, wherein a reflective layer is provided on a surface of
the unit substrate and between the surface and the unit adhesion
material layer, the reflective layer reflecting the light including
the predetermined wavelength.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermally-assisted magnetic
recording head constituted by joining a light source unit including
a light source that emits light for performing thermally-assisted
magnetic recording and a slider, and relates to a method for
manufacturing the thermally-assisted magnetic recording head.
2. Description of the Related Art
As the recording densities of magnetic recording apparatuses become
higher, as represented by magnetic disk apparatuses, further
improvement has been required in the performance of thin-film
magnetic heads and magnetic recording media. The magnetic recording
medium is generally a kind of discontinuous body of magnetic grains
gathered together, and each of the magnetic grains has an almost
single magnetic domain structure. Here, one record bit consists of
a plurality of the magnetic grains. Therefore, in order to improve
the recording density, it is necessary to decrease the size of the
magnetic grains and reduce irregularity in the boundary of the
record bit. However, the decrease in size of the magnetic grains
raises a problem of degradation in thermal stability of the
magnetization due to the decrease in volume.
As a measure against the thermal stability problem, it may be
possible to increase the magnetic anisotropy energy K.sub.U of the
magnetic grains. However, the increase in energy K.sub.U causes the
increase in anisotropic magnetic field (coercive force) of the
magnetic recording medium. Whereas, the intensity of write field
generated from the thin-film magnetic head is limited almost by the
amount of saturation magnetic flux density of the soft-magnetic
material of which the magnetic core of the head is formed. As a
result, the head cannot write data to the magnetic recording medium
when the anisotropic magnetic field of the medium exceeds the write
field limit.
Recently, as a method for solving the problem of thermal stability,
so-called a thermally-assisted magnetic recording technique is
proposed. In the technique, a magnetic recording medium formed of a
magnetic material with a large energy K.sub.U is used so as to
stabilize the magnetization, then anisotropic magnetic field of a
portion of the medium, where data is to be written, is reduced by
heating the portion; just after that, writing is performed by
applying write field to the heated portion.
In this thermally-assisted magnetic recording technique, there is
generally used a method in which a magnetic recording medium is
irradiated and thus heated with a light such as near-field light
(NF-light). In this case, it is significantly important to stably
supply a light with a sufficiently high intensity at a desired
position. However, from the beginning, more significant problem to
be solved exists in where and how a light source with a
sufficiently high output of light should be disposed inside a
head.
As for the setting of the light source, for example, U.S. Pat. No.
7,538,978 B2 discloses a configuration in which a laser unit
including a laser diode is mounted on the back surface of a slider,
and US Patent Publication No. 2008/0056073 A1 discloses a
configuration in which a structure of a laser diode element with a
monolithically integrated reflection mirror is mounted on the back
surface of a slider. Further, US Patent Publication No.
2005/0213436 A1 discloses a structure of slider that is formed
together with a semiconductor laser, and Robert E. Rottmayer et al.
"Heat-Assisted Magnetic Recording" IEEE TRANSACTIONS ON MAGNETICS,
Vol. 42, No. 10, p. 2417-2421 (2006) discloses a configuration in
which a diffraction grating is irradiated with a light generated
from a laser unit provided within a drive apparatus.
As described above, various types of the setting of the light
source are suggested. However, the present inventors propose a
thermally-assisted magnetic recording head with a "composite slider
structure" which is constituted by joining a light source unit
provided with a light source to the end surface (back surface) of a
slider provided with a magnetic head element, the end surface being
opposite to the opposed-to-medium surface of the slider. The
"composite slider structure" is disclosed in, for example, US
Patent Publication No. 2008/043360 A1 and US Patent Publication No.
2009/052078 A1. The advantages of the thermally-assisted magnetic
recording head with the "composite slider structure" are as
follows:
a) The head has an affinity with the conventional manufacturing
method of thin-film magnetic heads because the opposed-to-medium
surface and the element-integration surface are perpendicular to
each other in the slider.
b) The light source can avoid suffering mechanical shock directly
during operation because the light source is provided far from the
opposed-to-medium surface.
c) The light source such as a laser diode and the magnetic head
elements can be evaluated independently of each other; thus the
degradation of manufacturing yield for obtaining the whole head can
be avoided; whereas, in the case that all the light source and
magnetic head elements are provided within the slider, the
manufacturing yield rate for obtaining the whole head is likely to
decrease significantly due to the multiplication of the process
yield for the light-source and the process yield for the
slider.
d) The head can be manufactured with reduced man-hour and at low
cost, because of no need to provide the head with optical
components such as a lens or prism which are required to have much
high accuracy, or with optical elements having a special structure
for connecting optical fibers or the like.
In the head having the "composite slider structure", light emitted
from the light-emission center located in the light-emitting
surface of the light source needs to be incident accurately on the
light-receiving end of an optical system such as a waveguide
located on the back surface of the slider to achieve sufficiently
high light use efficiency. Therefore, the light-emission center and
the light-receiving end need to be aligned with each other as
accurately as possible both in the track width direction and the
direction perpendicular to the track width direction. It is
preferable that the accuracy of the alignment be within .+-.1
micrometer (.mu.m) in actual manufacturing. Therefore, it is an
important issue to properly align and bond a light source unit and
a slider in manufacturing of a head having the "composite slide
structure".
In particular, bonding of the light source unit and the slider
needs to be performed in such a way that the bonding does not
adversely affect the elements in the head while maintaining the
achieved alignment accuracy. For example, if an organic adhesive
such as an ultraviolet (UV) curable resin is used for the bonding,
some measures should be taken to prevent the light source unit and
the slider from being displaced with respect to each other in the
process of curing the adhesive. In addition, considerations need to
be made to prevent relative misalignment between the light source
unit and the slider during use of the head after the adhesive has
cured and bonding has been completed.
On the other hand, there is a method for bonding the light source
unit and the slider by using an alloy as solder to join them with
higher adhesive strength and less change with time. However, in the
conventional soldering methods, the light source unit and the
slider are heated in a heating unit in the process of melting
solder, and are therefore exposed to a considerably high
temperature for certain duration of time. Especially, the slider
typically includes an electromagnetic transducer for writing data
and an MR element for reading data. When these magnetic head
elements are heated to a high temperature higher than 200.degree.
C., for example, the magnetic pole tends to thermally expand to
protrude to an undesirable extent or an MR multilayer structure
tends to degrade, which can result in defects. Furthermore,
considerations need to be made so that the bonding in the light
source unit between the unit substrate and the light source can
avoid being adversely affected by the heating of the light source
unit and the slider in the process of melting the solder.
For these reasons, it is critically important to find a more
appropriate method for bonding the light source unit and the slider
in manufacturing of a head having the "composite slider
structure".
SUMMARY OF THE INVENTION
Some terms used in the specification will be defined before
explaining the present invention. In a layered structure or an
element structure formed in the element-integration surface of a
slider substrate or in the source-installation surface of a unit
substrate of the magnetic recording head according to the present
invention, when viewed from a standard layer or element, a
substrate side is defined as "lower" side, and the opposite side as
an "upper" side. Further, "X-, Y- and Z-axis directions" are
indicated in some figures showing embodiments of the head according
to the present invention as needed. Here, Z-axis direction
indicates above-described "up-and-low" direction, and +Z side
corresponds to a trailing side and -Z side to a leading side. And
Y-axis direction indicates a track width direction, and X-axis
direction indicates a height direction.
According to the present invention, a method for manufacturing a
thermally-assisted magnetic recording head is provided, in which a
light source unit including a light source provided in a unit
substrate and a slider including an optical system provided in a
slider substrate are joined with each other, wherein the unit
substrate is made of a material transmitting light having a
predetermined wavelength and a unit adhesion material layer is
formed on a surface of one or each of the light source unit and the
slider, the unit adhesion material layer (solder layer) containing
a material selected from a group consisting of Sn (tin), Sn alloy,
Pb (lead) alloy and Bi (bismuth) alloy. This manufacturing method
comprises the steps of:
aligning the light source unit and the slider with each other in
such a way that a light generated from the light source can enter
the optical system and the unit adhesion material layer is
sandwiched between the light source unit and the slider;
causing a light including the predetermined wavelength to enter the
unit substrate to melt the unit adhesion material layer; and
bonding the light source unit and the slider with each other.
In the above-described manufacturing method of the
thermally-assisted magnetic recording head, since the unit adhesion
material layer can be melted by the light that includes a
predetermined wavelength and has been transmitted through the unit
substrate in bonding of the light source unit and the slider, high
alignment accuracy can be achieved while joining with higher
bonding strength and less change with time can be achieved.
Further, the use of the unit adhesion material layer made of Sn, Sn
alloy, Pb alloy or Bi alloy enables joining that does not adversely
affect the joining between the unit substrate and the light source
by a light-source adhesion material layer (solder layer).
Further, in the manufacturing method according to the present
invention, it is preferable that the unit adhesion material layer
contains a material selected from a group consisting of Sn, SnAu,
SnCu, SnAl, SnSi, SnGe, SnMg, SnPb, SnAg, SnZn, SnBi, SnNi, SnPt,
PbAu, PbMg, PbBi and BiAu. Furthermore, the unit adhesion material
layer is preferably made of a material having a melting point lower
than a melting point of a light-source adhesion material layer used
for joining the light source to an electrode provided on the unit
substrate, and is more preferably made of a material having a
melting point lower, by 30.degree. C. or more, than the melting
point of the light-source adhesion material layer. Further, a
reflective layer is preferably provided on a surface of the unit
substrate opposed to the slider substrate when joined to the
slider, the reflective layer reflecting the light including the
predetermined wavelength.
Furthermore, in the manufacturing method according to the present
invention, it is preferable that the light source is activated, and
the light source unit and the slider are aligned in such a way that
the light generated from the light source enters the optical
system. This alignment method is a so-called active alignment
method, which can achieve high alignment accuracy. Furthermore, it
is also preferable that the melting of the unit adhesion material
layer by the entering of the light including the predetermined
wavelength is assisted by heating the unit adhesion material layer
to a high temperature with a heat generated from the activated
light source.
In the alignment using the active alignment method according to the
present invention, it is preferable that the unit adhesion material
layer is repeatedly melted by causing the lights including the
predetermined wavelength to enter the unit substrate from different
directions, to correct variations in relative positions of the
light source unit and the slider caused by the melting of the unit
adhesion material layer. In this preferable case, it is also
preferable that the amount of displacement of the light source unit
and the slider with respect to each other is obtained beforehand in
the case that the unit adhesion material layer is irradiated with a
predetermined one shot of each of the lights from different
directions, then the number of shots of each of the lights from
different directions is determined.
Further, in the manufacturing method according to the present
invention, it is preferable that the slider comprises a magnetic
head element configured to write and/or read data, and the slider
substrate is made of a material having a lower thermal conductivity
than a material of the unit substrate so that conduction of a heat
generated by the entering of the light including the predetermined
wavelength to the magnetic head element is limited. By controlling
the thermal conductivity of the slider substrate, irradiating the
unit adhesion material layer with the light that includes the
predetermined wavelength and has passed through the unit substrate
and melting the layer, adverse influence of heat generated by the
irradiation on the magnetic head element provided in the slider can
be avoided. Further, it is also preferable that, during the
alignment, a holding means to hold the light source unit is used as
a heatsink for the heat generated by the entering of the light
including the predetermined wavelength.
Further, in the manufacturing method according to the present
invention, it is preferable that the unit substrate is made of a
material selected from a group consisting of Si (silicon), GaAs
(gallium arsenide) and SiC (silicon carbide), and a YAG laser light
is used as the light including the predetermined wavelength. Here,
YAG is the name of a crystal having a garnet structure, made of a
composite oxide (Y.sub.3Al.sub.5O.sub.12) of Y (yttrium) and Al
(aluminum). Nd-YAG laser light can be obtained by using a YAG
crystal in which a several percent of Y is replaced with Nd
(neodymium) as the laser medium, and is widely used in research,
industrial, medical and other applications.
Furthermore, in the manufacturing method according to the present
invention, it is preferable that, as the light including the
predetermined wavelength, a circularly- or elliptically-polarized
light is preferably used, and a P-polarized light is also
preferably used. By using such light, the light that includes the
predetermined wavelength and has entered the unit substrate can be
more absorbed into the unit substrate. As a result, the unit
adhesion material layer can be melted more efficiently, thereby
achieving good joining.
According to the present invention, a thermally-assisted magnetic
recording head is further provided, which comprises:
a light source unit comprising: a unit substrate made of a material
transmitting light having a predetermined wavelength; and a light
source provided in a source-installation surface of the unit
substrate; and
a slider comprising: a slider substrate made of a material having a
lower thermal conductivity than a material of the unit substrate; a
magnetic head element configured to write and/or read data and
provided in an element-integration surface of the slider substrate;
and an optical system configured to propagate a light from the
light source toward a magnetic recording medium and provided in the
element-integration surface,
the light source unit and the slider being bonded by an adhesion
material layer melted and solidified with a light that includes the
predetermined wavelength and has passed through the unit substrate,
and
the unit adhesion material layer containing a material selected
from a group consisting of Sn (tin), Sn alloy, Pb (lead) alloy and
Bi (bismuth) alloy.
Further objects and advantages of the present invention will be
apparent from the following description of preferred embodiments of
the invention as illustrated in the accompanying figures. In each
figure, the same element as an element shown in other figure is
indicated by the same reference numeral. Further, the ratio of
dimensions within an element and between elements becomes arbitrary
for viewability.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view schematically illustrating a
structure of a major part in one embodiment of a magnetic disk
apparatus according to the present invention;
FIG. 2 shows a perspective view schematically illustrating a
structure of a major part in one embodiment of a head gimbal
assembly (HGA) according to the present invention;
FIG. 3 shows a perspective view illustrating one embodiment of the
thermally-assisted magnetic recording head according to the present
invention;
FIG. 4 shows a perspective view illustrating the structure of a
laser diode and the state of joining the laser diode to a unit
substrate;
FIG. 5 shows a cross-sectional view taken by plane A in FIG. 3,
schematically illustrating the configuration of a head element and
its vicinity in the thermally-assisted magnetic recording head;
FIG. 6 shows a perspective view schematically illustrating the
configuration of a waveguide, a near-field light (NF-light)
generator and a main magnetic pole;
FIGS. 7a to 7c show perspective views schematically illustrating an
embodiment of a method for manufacturing the thermally-assisted
magnetic recording head according to the present invention, in
which a light source unit is joined to a slider;
FIGS. 8a to 8c show perspective views schematically illustrating
another embodiment of the method for manufacturing the
thermally-assisted magnetic recording head according to the present
invention, in which a light source unit and a slider are joined
with each other; and
FIG. 9 shows a schematic view illustrating an experimental system
used in the simulation for studying the effect of polarization of
Nd-YAG laser light on absorption of the Nd-YAG laser light into the
unit substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a perspective view schematically illustrating a
structure of a major part in one embodiment of a magnetic disk
apparatus according to the present invention. FIG. 2 shows a
perspective view schematically illustrating a structure of a major
part in one embodiment of a head gimbal assembly (HGA) according to
the present invention. In FIG. 2, the side of the HGA opposed to
the surface of a magnetic disk is presented as the upper side.
A magnetic disk apparatus as a magnetic recording apparatus shown
in FIG. 1 includes: a plurality of magnetic disks 10 rotating
around a rotational axis of a spindle motor 11; an assembly
carriage device 12 provided with a plurality of drive arms 14
thereon; an HGA 17 attached on the top end portion of each drive
arm 14 and provided with a thermally-assisted magnetic recording
head 21; and a recording/reproducing and light-emission control
circuit 13 for controlling write/read operations of the
thermally-assisted magnetic recording head 21 and further for
controlling the emission operation of a laser diode as a light
source that generates laser light for thermally-assisted magnetic
recording, which will be described later.
The magnetic disk 10 is, in the present embodiment, designed for
perpendicular magnetic recording, and has a structure in which, for
example, sequentially stacked on a disk substrate is: a
soft-magnetic under layer; an intermediate layer; and a magnetic
recording layer (perpendicular magnetization layer). The assembly
carriage device 12 is a device for positioning the
thermally-assisted magnetic recording head 21 above a track formed
on the magnetic recording layer of the magnetic disk 10, on which
recording bits are aligned. In the apparatus, the drive arms 14 are
stacked in a direction along a pivot bearing axis 16 and can be
angularly swung around the axis 16 by a voice coil motor (VCM) 15.
The structure of the magnetic disk apparatus according to the
present invention is not limited to that described above. For
instance, the number of each of magnetic disks 10, drive arms 14,
HGAs 17 and sliders 21 may be one.
Referring to FIG. 2, a suspension 20 in the HGA 17 includes a load
beam 200, a flexure 201 with elasticity fixed to the load beam 200,
a base plate 202 provided on the base portion of the load beam 200,
and a wiring member 203 provided on the flexure 201 and made up of
lead conductors and connection pads electrically joined to both
ends of the lead conductors. The thermally-assisted magnetic
recording head 21 is fixed to the flexure 201 at the top end
portion of the suspension 20 so as to face the surface of each
magnetic disk 10 with a predetermined space (flying height). Here,
an aperture 2010 is provided in the flexure 201; the
thermally-assisted magnetic recording head 21 is fixed in such a
way that a part of the head 21 (light source unit 23 in FIG. 3)
protrudes from the opposite side of the aperture 2010. Moreover,
one ends (connection pads) of the wiring member 203 are
electrically connected to terminal electrodes of the
thermally-assisted magnetic recording head 21. The structure of the
suspension 20 is not limited to the above-described one. An IC chip
for driving the head may be mounted midway on the suspension 20,
though not shown.
FIG. 3 shows a perspective view illustrating one embodiment of the
thermally-assisted magnetic recording head 21 according to the
present invention.
As shown in FIG. 3, a thermally-assisted magnetic recording head 21
is constituted by aligning and joining a light source unit 23 that
includes a laser diode 40 and a slider 22 that includes an optical
system 31. The slider 22 includes: a slider substrate 220 having an
air bearing surface (ABS) 2200 processed so as to provide an
appropriate flying height; and a head element part 221 formed on an
element-integration surface 2202 that is perpendicular to and
adjacent to the ABS 2200. While, the light source unit 23 includes:
a unit substrate 230 having an joining surface 2300; and a laser
diode 40 as a light source provided on a source-installation
surface 2302 that is perpendicular to and adjacent to the joining
surface 2300. The slider 22 and the light source unit 23 are bonded
to each other in such a way that the back surface 2201 of the
slider substrate 220 and the joining surface 2300 of the unit
substrate 230 are opposed to each other and sandwich a solder layer
58 as a unit adhesion material.
Here, the unit substrate 230 is made of a material that transmits a
laser light used for bonding the light source unit 23 and the
slider 22 together, which will be described in detail later. If
Nd-YAG laser light (wavelength: 1064 nanometers (nm)), which will
be described later, is used, the unit substrate 230 is preferably
made of a material that has a transmittance greater than or equal
to 50% at a wavelength of 1064 nm, such as Si (transmittance: 67%),
GaAs (transmittance: 66%), or SiC (transmittance: 80%). This
ensures the bonding between the light source unit 23 and the slider
22 using laser light, which will be described later.
The slider substrate 220 is preferably made of a material that has
a lower thermal conductivity than the material of the unit
substrate 230 for reasons that will be described later. For
example, if the unit substrate 230 is made of Si (thermal
conductivity: 168 W/(mK)), the slider substrate 220 is preferably
made of a material such as AlTic (Al.sub.2O.sub.3-Tic) (thermal
conductivity: 19.0 W/(mK)) or SiO.sub.2 (thermal conductivity: 10.7
W/(mK)). This can minimize adverse influence of heat on a magnetic
head element 32, the heat being generated by laser irradiation used
for bonding between the light source unit 23 and the slider 22.
Further, the solder layer 58 is a unit adhesion material layer
melted and solidified by irradiating the unit substrate 230 with
laser light. The solder layer 58 joins the light source unit 23 to
the slider 22. The solder layer 58 is preferably made of an alloy
having a melting point lower than 400.degree. C., more preferably
lower than or equal to 250.degree. C. Further, the solder layer 58,
which is the unit adhesion material layer, is preferably made of a
material having a melting point lower than a solder layer 52 (FIG.
4), which is a light-source adhesion material layer used for
joining the laser diode 40 to the unit electrode 4100 provided on
the unit substrate 230, more preferably a material having a melting
point lower than the solder layer 52 by 30.degree. C. or more, as
will be described later in detail. For example, if the solder layer
52 is made of an AuSn alloy (containing 80 weight % of Au), the
melting point of the solder layer 52 is in the range of
approximately 280 to 300.degree. C. In that case, the solder layer
58 may be made of Sn, or a Sn alloy, a Pb alloy or a Bi alloy which
have a melting point at the eutectic composition (a eutectic point)
lower than or equal to 250.degree. C. Here, the solder layer 58 has
a higher thermal conductivity than the slider substrate 220, and
heat generated by laser irradiation can be used more in melting the
solder layer 58 than in being conducted to the slider substrate
220. The thickness of the solder layer 58 may be in the range of
approximately 0.05 to 5.0 micrometers (.mu.m), for example.
As also shown in FIG. 3, in the slider 22, the head element part
221 formed on the element-integration surface 2202 of the slider 22
includes: a head element 32 constituted of a magnetoresistive (MR)
element 33 for reading data from the magnetic disk 10 (FIG. 1) and
an electromagnetic transducer 34 for writing data to the magnetic
disk; a spot-size converter 43 that receives a laser light emitted
from the laser diode 40, changes (reduces) the spot size of the
laser light, then guides the laser light into the waveguide 35; a
waveguide 35 that guides the laser light with changed spot size to
the head end surface 2210 as an opposed-to-medium surface or its
vicinity; a near-field light (NF-light) generator 36 that generates
NF-light for thermal assist; and an overcoat layer 38 formed on the
element-integration surface 2202 so as to cover the head element
32, the spot-size converter 43, the waveguide 35 and the NF-light
generator 36. Here, the spot-size converter 43, the waveguide 35
and the NF-light generator 36 constitute the optical system 31 for
generating NF-light in the head 21 (head element part 221).
Further, the slider 22 includes a pair of terminal electrodes 370
and a pair of terminal electrodes 371, which are provided for the
head element 32, formed on the end surface 2211 of the head element
part 221, the end surface 2211 being on the side opposite to the
opposed-to-medium surface (head end surface) 2210. Further, the
light source unit 23 includes a terminal electrode 410 connected
electrically to an n-electrode layer 40a of the laser diode 40 and
provided on the source-installation surface 2302. The light source
unit 23 further includes a terminal electrode 411 connected
electrically to a p-electrode layer 40i of the laser diode 40 and
provided on the p-electrode layer 40i. These terminal electrodes
370, 371, 410 and 411 are electrically connected to the connection
pads of the wiring member 203 provided on the flexure 201 by wire
bonding, solder ball bonding (SBB), or the like.
One ends of the MR element 33, the electromagnetic transducer 34
and the NF-light generator 36 reach the head end surface 2210 as an
opposed-to-medium surface. Here, the head end surface 2210 and the
ABS 2200 constitute the whole opposed-to-medium surface of the
thermally-assisted magnetic recording head 21. During actual write
and read operations, the thermally-assisted magnetic recording head
21 aerodynamically flies above the surface of the rotating magnetic
disk with a predetermined flying height. Thus, the ends of the MR
element 33 and electromagnetic transducer 34 face the surface of
the magnetic record layer of the magnetic disk 10 with a
appropriate magnetic spacing. Then, MR element 33 reads data by
sensing signal magnetic field from the magnetic record layer, and
the electromagnetic transducer 34 writes data by applying signal
magnetic field to the magnetic record layer. When writing data,
laser light, which is generated from the laser diode 40 of the
light source unit 23 and propagates through the spot-size converter
43 and the waveguide 35, is changed into NF-light in the NF-light
generator 36. Then, a portion to be written of the magnetic
recording layer is irradiated and thus heated with the NF-light. As
a result, the anisotropic magnetic field (coercive force) of the
portion is decreased to a value that enables writing; thus the
thermally-assisted magnetic recording can be achieved by applying
write field with use of the electromagnetic transducer 34 to the
anisotropic-field-decreased portion.
Referring also to FIG. 3, a spot-size converter 43 is an optical
element which receives laser light emitted from the laser diode 40
at its light-receiving end surface 430 having a width W.sub.SC in
the track width direction (the Y-axis direction), converts the
laser light to laser light with a smaller spot diameter with a low
loss while maintaining a single mode, and then guides the converted
laser light to a light-receiving end surface 352 of the waveguide
35. Here, the single-mode is a mode in which the laser light
propagating within the spot-size converter 43 has a beam
cross-section with a shape of circle or ellipsoid, and the light
intensity distribution in the cross-section is single-peaked,
especially a Gaussian. Laser light with a single mode can become a
stable laser light with an intended intensity even in the case that
the spot size of the laser light is converted into a smaller one
due to the propagation through the spot-size converter 43. The
spot-size converter 43 in the present embodiment includes a lower
propagation layer 431 and an upper propagation layer 432. The lower
propagation layer 431 has a width in the track width direction
(Y-axis direction) that gradually decreases from the width W.sub.SC
along the traveling direction (-X direction) of laser light
incident through the light-receiving end surface 430. The upper
propagation layer 432 is stacked on the lower propagation layer 431
and has a width in the track width direction (Y-axis direction)
that more steeply decreases from the width W.sub.SC along the
traveling direction (-X direction) of laser light than the lower
propagation layer 431. Laser light incident through the
light-receiving end surface 430 is converted to laser light with a
smaller spot size as the laser light propagates through the layered
structure, and reaches the light-receiving end surface 352 of the
waveguide 35.
The width W.sub.SC of the spot-size converter 43 at the
light-receiving end surface 430 may be in the range of
approximately 1 to 10 .mu.m, for example. The thickness T.sub.SC
(in Z-axis direction) at the light-receiving end surface 430 may be
in the range of approximately 1 to 10 .mu.m, for example. The
light-receiving end surface 430 is preferably inclined at a
predetermined acute angle, for example at an angle of approximately
4.degree. (degrees) with respect to the end surface 400 including
the light-emission center 4000 of the laser diode 40. Such angle
prevents laser light reflected by the light-receiving end surface
430 from returning to the light-emission center 4000. The spot-size
converter 43 is made of a material with a refractive index higher
than the refractive index n.sub.OC of the constituent material of
the surrounding overcoat layer 38. The spot-size converter 43 can
be formed from the same dielectric material as the waveguide 35,
which will be described below. In the case, the spot-size converter
43 and the waveguide 35 may be formed integrally.
The waveguide 35 in the present embodiment extends in parallel with
the element-integration surface 2202 from the light-receiving end
surface 352 that receives laser light emitted from the spot-size
converter 43 to the end surface 350 on the head end surface 2210
side. Here, the end surface 350 may be a portion of the head end
surface 2210, or may be recessed from the head end surface 2210
with a predetermined distance. A portion of one side surface of the
waveguide 35 near the end surface 350 faces a NF-light generator
36. This allows laser light (waveguide light) incident through the
light-receiving end surface 352 and traveling through the waveguide
35 to reach the portion facing the NF-light generator 36, thereby
to be coupled with the generator 36.
Referring again to FIG. 3, a unit electrode 4100 is provided on the
source-installation surface 2302 of the unit substrate 230 of the
light source unit 23. The unit electrode 4100 may be formed by a
foundation layer of a material such as Ta or Ti with a thickness of
approximately 10 nm, for example, and a conducting layer of a
conductive material such as Au, Cu or an alloy of Au with a
thickness in the range of approximately 1 to 5 .mu.m, for example.
The terminal electrode 410 is electrically connected with the
n-electrode layer 40a of the laser diode 40 through the unit
electrode 4100, the n-electrode layer 40a having a surface contact
with the unit electrode 4100. The terminal electrode 411 may be a
conductive layer formed on the p-electrode layer 40i of the laser
diode 40, and made of, for example, Au, Cu or Au alloy with a
thickness in the range of approximately 1 to 5 .mu.m. When a
predetermined voltage is applied between the n-electrode layer 40a
and a p-electrode layer 40i of the laser diode 40 through these
terminal electrodes 410 and 411, the laser diode 40 oscillates and
laser light is emitted from the light-emission center 4000.
Furthermore, preferably a reflective layer 57 is provided on the
joining surface 2300 of the unit substrate 230. The reflective
layer 57 reflects light 78 such as Nd-YAG laser light (FIG. 7c)
that is used in joining the light source unit 23 to the slider 22
and is propagating through the unit substrate 230 so that a
sufficient amount of the light 78 is absorbed into the unit
substrate 230, as will be described later in detail.
As also shown in FIG. 3, the slider substrate 220 is, for example,
a so-called Femto slider having a thickness (in X-axis direction)
T.sub.SL of 230 .mu.m, a width W.sub.SL of 700 .mu.m in the track
width direction (Y-axis direction), and a length L.sub.SL (in
Z-axis direction) of 850 .mu.m. The Femto slider is commonly used
as the substrate of a thin-film magnetic head capable of achieving
a high recording density and is the smallest in standardized size
among the currently used sliders. On the other hand, the unit
substrate 230 is somewhat smaller than the slider substrate 220. In
particular, the width W.sub.UN of the unit substrate 230 in the
track width direction (Y-axis direction) is preferably greater than
or equal to the width W.sub.LA of the laser diode 40 in the track
width direction (Y-axis direction), and is preferably smaller than
the width W.sub.SL of the slider substrate 220. The width setting
enables a laser light for melting the solder layer 58 to reach the
solder layer 58 by being transmitted through the unit substrate 230
without irradiating and heating the slider substrate 220 with the
laser light during the transmission, as described in detail later.
Considering the requirements described above, the unit substrate
230 may have a thickness T.sub.UN (in X-axis direction) of 320
.mu.m, a width W.sub.UN in the track width direction of 350 .mu.m,
and a length L (in Z-axis direction) of 250 .mu.m, for example.
As described above, the thermally-assisted magnetic recording head
21 has the structure in which the slider 22 and the light source
unit 23 are interconnected. Thus, the slider 22 and the light
source unit 23 can be separately fabricated and then combined
together to fabricate the head 21. Consequently, the production
yield of the entire heads is about the same as the production yield
of the sliders 22 if performance evaluation of the light source
units 23 is performed prior to the fabrication of the heads and
only good light source units 23 are used for the fabrication of the
heads. Thus, the reduction of production yield of the entire heads
due to the rejection rate of the laser diodes 40 can be avoided.
Furthermore, since the light source unit 23 is attached to the back
surface 2201 of the slider 22 which is opposite to the ABS 2200 of
the slider 22, the laser diode 40 can be always disposed in a
location far from the ABS 2200. As a result, direct mechanical
impact on the laser diode 40 in operation can be avoided. Moreover,
since the ABS 2200 of the slider 22 is perpendicular to the
element-integration surface 2202, the slider 22 has a high affinity
for conventional thin-film magnetic head fabrication processes.
Since an optical part that requires a considerably high accuracy
such as an optical pickup lens or an optical part that requires a
special structure for connection such as an optical fiber do not
need to be provided in the thermally-assisted magnetic recording
head 21, the number of man-hours and thus costs can be reduced.
FIG. 4 shows a perspective view illustrating the structure of the
laser diode 40 and the state of joining the laser diode 40 to the
unit substrate 230.
According to FIG. 4, the laser diode 40 is, in the present
embodiment, of edge-emitting type. As the laser diode 40, InP base,
GaAs base or GaN base diodes can be utilized, which are usually
used for communication, optical disk storage, material analysis or
the like. The wavelength .lamda..sub.L of the emitted laser light
may be, for example, in the range of approximately 375 nm to 1.7
.mu.m. For example, a laser diode of InGaAsP/InP quaternary mixed
crystal can be used, in which possible wavelength region is set to
be from 1.2 to 1.67 .mu.m. Here, the laser diode 40 shown in FIG. 4
has a multilayered structure in which sequentially stacked from the
unit substrate 230 side are: an n-electrode layer 40a having a
surface contact and bonded with the unit electrode 4100; an n-GaAs
substrate 40b; an n-InGaAlP clad layer 40c; the first InGaAlP guide
layer 40d; an active layer 40e formed of multiquantum well
(InGaP/InGaAlP) or the like; the second InGaAlP guide layer 40f; an
p-InGaAlP clad layer 40g; a p-electrode base layer 40h; and a
p-electrode layer 40i.
The n-electrode layer 40a and the p-electrode layer 40i may be
formed of, for example, Au or Au alloy with thickness of
approximately 5 .mu.m. Alternatively, the p-electrode layer 40i may
be bonded to the unit substrate 4100 by turning the laser diode 40
upside down. Further, on the front and rear cleaved surfaces of the
multilayered structure of the laser diode 40, respectively formed
are reflective layers 510 and 511 for exciting the oscillation by
total reflection. The outer surface of the reflective layer 510 on
the joining surface 2300 side is a light-emission surface 400, and
the light-emission surface 400 includes a light-emission center
4000 at the position of the active layer 40e. The laser diode 40
has a width W.sub.LA of, for example, approximately 150 to 250
.mu.m. The length L.sub.LA of the laser diode 40 corresponds
approximately to a cavity length that is the distance between the
reflective layers 510 and 511, and is, for example, 300 .mu.m. The
length L.sub.LA is preferably 300 .mu.m or more in order to obtain
a sufficient high output. Further, the height T.sub.LA of the laser
diode 40 is, for example, approximately 60 to 200 .mu.m.
An electric source provided within the magnetic disk apparatus can
be used for driving the laser diode 40. In fact, the magnetic disk
drive apparatus usually has an electric source with applying
voltage of, for example, approximately 2 to 5V, which is sufficient
for the laser oscillation. Even in the case that the amount of
electric power consumption of the laser diode 40 is, for example,
in the vicinity of one hundred mW, the amount can be covered
sufficiently by the electric source provided within the magnetic
disk apparatus.
Referring again to FIG. 4, the n-electrode layer 40a of the laser
diode 40 can be soldered to the unit electrode 4100 on the unit
substrate 230 by the solder layer 52, which is a light-source
adhesion material layer. The solder layer 52 is preferably made of
a material having a melting point higher than the solder layer 58
(FIG. 3), which is a unit adhesion material layer, as will be
described later in detail. For example, if the solder layer 58 is
made of Sn (tin, which has a melting point of 231.degree. C.), the
solder layer 52 may be made of an AuSn alloy (containing 80 weight
% of Au and having a melting point in the range of approximately
280 to 300.degree. C.). If the solder layer 58 is made of SnPb
(having a melting point of 183.degree. C.), the solder layer 52 may
be made of an AuSn alloy (containing 80 weight % of Sn and having a
melting point of approximately 220.degree. C.).
Here, preferably the laser diode 40 is bonded onto the unit
substrate 230 in such a way that the distance D.sub.REC (in X-axis
direction) between the light-emitting surface 400 of the laser
diode 40 and the joining surface 2300 is 0 or more, and 5 .mu.m or
less. Since the distance D.sub.REC is greater than or equal to 0,
the laser diode 40 does not protrude from the light source unit 23.
Consequently, the laser diode 40 is prevented from being subjected
to excessive mechanical stress and damage during bonding.
Furthermore, since the direction D.sub.REC is less than or equal to
5 .mu.m, the distance between the light-emission center 4000 and
the light-receiving end surface 430 of the optical system 31 (FIG.
3) of the slider 22 is sufficiently small and therefore a high
light use efficiency can be provided.
FIG. 5 shows a cross-sectional view taken by plane A in FIG. 3,
schematically illustrating the configuration of the head element 32
and its vicinity in the thermally-assisted magnetic recording head
21.
As shown in FIG. 5, the MR element 33 is formed on a base layer 380
that is formed of an insulating material such as Al.sub.2O.sub.3
(alumina), SiO.sub.2 and stacked on the element-integration surface
2102. The MR element 33 includes: an MR multilayer 332; and a lower
shield layer 330 and an upper shield layer 334 which sandwich the
MR multilayer 332 and an insulating layer 381 therebetween. The MR
multilayer 332 is a magneto-sensitive part for detecting signal
magnetic field by utilizing MR effect. The MR multilayer 332 may
be, for example: a current-in-plane giant magnetoresistive
(CIP-GMR) multilayer; a current-perpendicular-to-plane giant
magnetoresistive (CPP-GMR) multilayer; or a tunnel magnetoresistive
(TMR) multilayer. In the case that the MR multilayer 332 is a
CPP-CMZ multilayer or a TMR multilayer, the upper and lower shield
layers 334 and 330 act as electrodes as well as magnetic
shields.
Referring also to FIG. 5, the electromagnetic transducer 34 is
designed for perpendicular magnetic recording, and includes an
upper yoke layer 340, a main magnetic pole 3400, a write coil layer
343, a coil-insulating layer 344, a lower yoke layer 345, and a
lower shield 3450.
The upper yoke layer 340 is formed so as to cover the
coil-insulating layer 344, and the main magnetic pole 3400 is
formed on an insulating layer 385 made of an insulating material
such as Al.sub.2O.sub.3 (alumina). These upper yoke layer 340 and
main magnetic pole 3400 are magnetically connected with each other,
and acts as a magnetic path for converging and guiding magnetic
flux toward the magnetic recording layer (perpendicular
magnetization layer) of the magnetic disk 10 (FIG. 1), the magnetic
flux being excited by write current flowing through the write coil
layer 343. The main magnetic pole 3400 includes: a first main pole
portion 3400a reaching the head end surface 2210 and having a small
width W.sub.P (FIG. 6) in the track width direction; and a second
main pole portion 3400b located on the first main pole portion
3400a and at the rear (+X side) of the portion 3400a. The first
main pole portion 3400a has an end surface 3400e (FIG. 6) with a
shape of, for example, a rectangle, a square or a trapezoid on the
head end surface 2210. Here, the above-described width W.sub.P is
the length of an edge in the track width direction (Y-axis
direction) of the end surface 3400e, and defines the width of write
field distribution in the track width direction (Y-axis direction).
The width W.sub.P can be set to be, for example, 0.05 to 0.5 .mu.m.
The main magnetic pole 3400 is preferably formed of a soft-magnetic
material with a saturation magnetic flux density higher than that
of the upper yoke layer 340, which is, for example, an iron alloy
containing Fe as a main component, such as FeNi, FeCo, FeCoNi, FeN
or FeZrN. The thickness of the first main pole portion 3400a is,
for example, in the range of approximately 0.1 to 0.8 .mu.m.
The write coil layer 343 is formed on an insulating layer 385 made
of an insulating material such as Al.sub.2O.sub.3 (alumina), in
such a way as to pass through in one turn at least between the
lower yoke layer 345 and the upper yoke layer 340, and has a spiral
structure with a back contact portion 3402 as a center. The write
coil layer 343 is formed of a conductive material such as Cu
(copper). The write coil layer 343 is covered with a
coil-insulating layer 344 that is formed of an insulating material
such as a heat-cured photoresist and electrically isolates the
write coil layer 343 from the upper yoke layer 340. The write coil
layer 343 has a monolayer structure in the present embodiment;
however, may have a two or more layered structure or a helical coil
shape. Further, the number of turns of the write coil layer 343 is
not limited to that shown in FIG. 5, and may be, for example, in
the range from two to seven.
The back contact portion 3402 has a though-hole extending in X-axis
direction, and the waveguide 35 and insulating layers that covers
the waveguide 35 pass through the though-hole. In the though-hole,
the waveguide 35 is away at a predetermined distance of, for
example, at least 1 .mu.m from the inner wall of the back contact
portion 3402. The distance prevents the absorption of the waveguide
light by the back contact portion 3402.
The lower yoke layer 345 is formed on an insulating layer 383 made
of an insulating material such as Al.sub.2O.sub.3 (alumina), and
acts as a magnetic path for the magnetic flux returning from a
soft-magnetic under layer that is provided under the magnetic
recording layer (perpendicular magnetization layer) of the magnetic
disk 10. The lower yoke layer 345 is formed of a soft-magnetic
material, and its thickness is, for example, approximately 0.5 to 5
.mu.m. Further, the lower shield 3450 is a part of the magnetic
path, being connected with the lower yoke layer 345 and reaching
the head end surface 2210. The lower shield 3450 is opposed to the
main magnetic pole 3400 through the NF-light generator 36, and acts
for receiving the magnetic flux spreading from the main magnetic
pole 3400. The lower shield 3450 has a width in the track width
direction greatly larger than that of the main magnetic pole 3400.
This lower shield 3450 causes the magnetic field gradient between
the end portion of the lower shield 3450 and the first main pole
portion 3400a to become steeper. As a result, jitter of signal
output becomes smaller, and therefore, error rates during read
operations can be reduced. The lower shield 3450 is preferably
formed of a material with high saturation magnetic flux density
such as NiFe (Permalloy) or an iron alloy as the main magnetic pole
3400 is formed of.
Referring also to FIG. 5, laser light 53a, the spot size of which
the spot-size converter 43 changes (reduces), enters the waveguide
35 from the light-receiving end surface 352, and propagates through
the waveguide 35. The waveguide 35 extends from the light-receiving
end surface 352 to the end surface 350 on the head end surface 2210
side through the through-hole that is provided in the back contact
portion 3402 and extends in X-axis direction. Furthermore, the
NF-light generator 36 is a generator that transforms the laser
light (waveguide light) propagating through the waveguide 35 into
NF-light. A part on the head end surface 2210 side of the waveguide
35 and the NF-light generator 36 are provided between the lower
shield 3450 (lower yoke layer 345) and the main magnetic pole 3400
(upper yoke layer 340). Further, a portion of the upper surface
(side surface) of the waveguide 35 on the head end surface 2210
side is opposed to a portion of the lower surface (including a
propagative edge 360 (FIG. 6)) of the NF-light generator 36 with a
predetermined distance. The sandwiched portion between these
portions constitutes a buffering portion 50 having a refractive
index lower than that of the waveguide 35. The buffering portion 50
acts for coupling the laser light (waveguide light) that propagates
through the waveguide 35 with the NF-light generator 36. A detailed
explanation of the waveguide 35, the buffering portion 50 and the
NF-light generator 36 will be given later with reference to FIG.
6.
Further, also as shown in FIG. 5, an inter-element shield layer 39
is preferably provided between the MR element 33 and the
electromagnetic transducer 34 (lower yoke layer 345), sandwiched by
the insulating layers 382 and 383. The inter-element shield layer
39 plays a role for shielding the MR element 33 from the magnetic
field generated from the electromagnetic transducer 34, and may be
formed of a soft-magnetic material. Here, the above-described
insulating layers 381, 382, 383, 384, 385 and 386 constitute the
overcoat layer 38.
FIG. 6 shows a perspective view schematically illustrating the
configuration of the waveguide 35, the NF-light generator 36 and
the main magnetic pole 3400. In the figure, the head end surface
2210 is positioned at the left side, the surface 2210 including
positions where write field and NF-light are emitted toward the
magnetic recording medium.
As shown in FIG. 6, the configuration includes a waveguide 35 for
propagating laser light (waveguide light) 53b used for generating
NF-light toward the end surface 350, and ae NF-light generator 36
that receives the waveguide light 53b and generates NF-light NF.
Here, the waveguide 35 is formed of a material with a refractive
index n higher than the refractive index n.sub.OC of the
constituent material of the overcoat layer 38. This material design
causes the waveguide 35 to act as a core, and causes the overcoat
layer 38 to act as a clad. For example, in the case that the
wavelength .lamda..sub.L of the laser light is 600 nm and the
overcoat layer 38 is formed of Al.sub.2O.sub.3 (n=1.63), the
waveguide 35 can be formed of, for example, SiO.sub.XN.sub.Y
(n=1.7-1.85) or Ta.sub.2O.sub.5 (n=2.16). Further, a portion
sandwiched between a portion of the side surface 354 of the
waveguide 35 and a portion of the lower surface 362 of the NF-light
generator 36 constitutes a buffering portion 50. The buffering
portion 50 is formed of a dielectric material having a refractive
index lower than the refractive index of the waveguide 35, and
plays a role of coupling the waveguide light 53a with the NF-light
generator 36. For example, when the wavelength .lamda..sub.L of the
laser light is 600 nm and the waveguide 35 is formed of TaOx
(n=2.16), the buffering portion 50 can be formed of SiO.sub.2
(n=1.46) or Al.sub.2O.sub.3 (n=1.63). In the light source and
optical system as shown in FIGS. 3, 5 and 6, the laser light
emitted from the light-emission center 4000 of the laser diode 40
preferably has TM-mode polarization in which the oscillation
direction of electric field of the laser light is along Z-axis.
The optical system that is provided in the head element part 221
and generates light for thermal assist is not limited to the
above-described one. For example, as an alternative, there can be
available an optical system that use a NF-light generator having
another shape and structure, or an optical system in which a
plasmon antenna made of a metal piece is provided at the end of a
waveguide.
FIGS. 7a to 7c show perspective views schematically illustrating an
embodiment of a method for manufacturing the thermally-assisted
magnetic recording head 21 according to the present invention, in
which the light source unit 23 is joined to the slider 22.
As illustrated in FIG. 7a, first a solder layer 58 is formed on the
back surface 2201 of the slider 22 by a method such as vapor
deposition. The solder layer 58 is a unit adhesion material layer
for joining the light source unit 23 to the slider 22. As has been
described above, the solder layer 58 is preferably made of an alloy
having a melting point lower than 400.degree. C., more preferably
lower than or equal to 250.degree. C. The material of the solder
layer 58 that has a melting point lower than or equal to
250.degree. C. may be Sn (tin), an Sn alloy, a Pb (lead) alloy, or
a Bi (bismuth) alloy, which is selected from the group consisting
of Sn, SnAu, SnCu, SnAl, SnSi, SnGe, SnMg, SnPb, SnAg, SnZn, SnBi,
SnNi, SnPt, PbAu, PbMg, PbBi and BiAu.
The solder layer 58, which is a unit adhesion material layer, is
preferably made of a material having a melting point lower than the
solder layer 52 (FIG. 4), which is a light-source adhesion material
layer used for joining the laser diode 40 to the unit electrode
4100 provided on the unit substrate 230. The solder layer 58 is
more preferably made of a material having a melting point lower
than the solder layer 52 by 30.degree. C. or more. For example, if
the solder layer 52 is made of an AuSn alloy (containing 80 weight
% of Au), the melting point of the solder layer 52 will be in the
range of approximately 280 to 300.degree. C. The Sn, Sn alloy, Pb
alloy, and Bi alloy given above have melting points at the eutectic
composition (eutectic points) lower than or equal to 250.degree.
C., which is lower than the melting point of the solder layer 52 by
30.degree. C. or more. That is, any of these Sn, Sn alloy, Pb alloy
and Bi alloy is significantly preferable as the material of the
solder layer 58.
A solder layer 58' may be formed on the joining surface 2300 of the
light source unit 23 as a unit adhesion material layer.
Alternatively, the solder layers 58 and 58' may be provided on the
slider 22 and the light source unit 23, respectively. As has been
described with respect to FIG. 3, preferably a reflective layer 57
is provided on the joining surface 2300 of the unit substrate 230.
The reflective layer 57 reflects light 78 (FIG. 7c) such as Nd-YAG
laser light that is used in joining the light source unit 23 to the
slider 22 and is propagating through the unit substrate 230 so that
a sufficient amount of the light 78 is absorbed into the unit
substrate 230. The reflective layer 57 may be a layer of a metal,
such as Au, Al, an Au alloy, or an Al alloy, which has a high
reflectivity, has a thickness of approximately 0.05 to 1 .mu.m, for
example, and is formed on a foundation layer made of a material
such as Ta or Ti having a thickness of approximately 1 to 10 nm. If
the solder layer 58' is provided, the reflective layer 57 and the
solder layer 58' will be formed on the joining surface 2300 in
sequence. It is also preferable that a foundation layer of a
material such as Ta or Ti having a thickness of approximately 1 to
10 nm, for example, and an adhesion layer 57' of a material such as
Au, Al, an Au alloy, or an Al alloy having a thickness of
approximately 5 to 20 nm, for example, are formed on the back
surface 2201 of the slider substrate 220. In this case, the solder
layer 58 is formed on the adhesion layer 57'.
Then, the slider 22 is placed on a stage 70 of an alignment system
and the light source unit 23 is attached to a holding jig 71 of the
alignment system in such a manner that the joining surface 2300 of
the unit substrate 230 is opposed to the back surface 2201 of the
slider substrate 220. The positioning of the holding jig 71 can be
controlled in relation to the stage 70 with desired accuracy, for
example, an accuracy of .+-.1 .mu.m or higher in Y-axis and Z-axis
directions. Then a predetermined voltage is applied between
terminal electrodes 410 and 411 of the laser diode 40 provided on
the light source unit 23 to activate the laser diode 40 and to
cause the laser diode 40 to emit laser light 72 from its
light-emission center 4000. Here, the light source unit 23 and the
slider 22 are at a predetermined distance away from each other in
X-axis direction and are movable in Y-axis direction (the track
width direction) and Z-axis direction.
In the present embodiment, as illustrated in FIG. 7b, while the
light source unit 23 and the slider 22 are moved in Y-axis and
Z-axis directions with respect to each other, the laser diode 40 is
actually kept operating, and laser light 72 being emitted from the
light-emission center 4000 is monitored in real time by a
photodetector 74 provided on the head end surface 2210 side to
perform alignment. That is, the so-called active alignment method,
which can achieve high alignment accuracy, is used to align the
light source unit 23 with the slider 22. Specifically, laser light
72 emitted from the light-emission center 4000 of the light source
unit 23 is incident on the optical system 31 through the
light-receiving end surface 430 of the slider 22 and is detected by
the photodetector 74 as light 73 emitted from the end surface 350
(FIG. 6) of the waveguide 35 or from the end surface 36a (FIG. 6)
of the NF-light generator 36. The photodetector 74 is disposed in
such a manner that its light-receiving surface faces the end
surface 350 or 36a. Here, the position of the slider 22 and the
light source unit 23 at the time the largest monitor output is
obtained from the photodetector 74 is determined to be the
alignment completion position in YZ plane, the largest monitor
output indicating that the largest amount of laser light 72 is
incident on the light-receiving end surface 430.
Then, as shown in FIG. 7c, the holding jig 71 is brought close to
the stage 70 to reduce the distance between the light source unit
23 and the slider 22 in X-axis direction without changing the
determined relative positions of the light source unit 23 and the
slider 22 in YZ-plane, until the light source unit 23 contacts the
slider 22, thereby determining the relative positions of the light
source unit 23 and the slider 22. Here, the solder layer 58 (solder
layer 58') is sandwiched between the light source unit 23 and the
slider 22. Then the unit substrate 230 is irradiated with light 78
with a predetermined wavelength that passes the unit substrate 230,
causing the light 78 to enter the unit substrate 230. The light 78
entering the unit substrate 230 heats the unit substrate 230. In
doing so, heat generated in the unit substrate 230 and the light 78
that reached the reflective layer 57 and the solder layer 58 (58')
melt the solder layer 58 (58'). The solder layer 58 (58') then
solidifies. Thus the light source unit 23 is joined to the slider
22.
Here, if the reflective layer 57 is provided, light 78 propagating
through the unit substrate 230 is reflected by the reflective layer
57. In consequence, the light path of the light 78 in the unit
substrate 230 is lengthened and a sufficient amount of light 78 is
absorbed into the material of the unit substrate 230. Accordingly,
the unit substrate 230, especially the portion near the joining
surface 2300 of the unit substrate 230 is wholly heated to a
sufficiently high temperature. Consequently, the entire solder
layer (58') under the joining surface 2300 is sufficiently melted
and better joining can be achieved. The reflective layer 57 also
acts as an adhesion layer that increases the wettability of the
light source unit 23 to the solder layer 58.
The light 78 can be Nd-YAG laser light (which has a wavelength of
1064 nm) emitted from an Nd-YAG laser oscillator 76 through an
optical fiber 77. Here, YAG is the name of a crystal having a
garnet structure, made of a composite oxide
(Y.sub.3Al.sub.5O.sub.12) of Y (yttrium) and Al (aluminum). Nd-YAG
laser light can be obtained by using a YAG crystal in which a
several percent of Y is replaced with Nd (neodymium) as the laser
medium. The Nd-YAG laser light is widely used in research,
industrial, medical and other applications. If Nd-YAG laser light
is used as the light 78, the unit substrate 230 is made from a
material that has a transmittance higher than or equal to 50% at a
wavelength of 1064 nm, such as Si (transmittance: 67%), GaAs
(transmittance: 66%), or SiC (transmittance: 80%) so that the
solder layer 58 (solder layer 58') can be irradiated with a
sufficient amount of light 78 for melting which passes through the
unit substrate 230. The light 78 may be other type of laser light
such as YAG laser light other than Nd-YAG laser light, solid-state
laser light other than YAG laser light, or gas laser light such as
carbon dioxide gas laser light. In all cases, light that has a
wavelength that can pass through the unit substrate 230 and has
output power required for melting the solder layer 58 (solder layer
58') is used; or a material that can pass the wavelength of light
used is used to form the unit substrate 230.
Further, using the active alignment method to align the light
source unit 23 and the slider 22 with respect to each other can
reduce the output power or the irradiation time required for
melting of the light 78. According to the active alignment method,
the laser diode 40 is kept operating and radiating considerable
heat during the alignment process until irradiation with the light
78, as stated above. The solder layer 58 (solder layer 58') has
already been heated by the heat to a temperature significantly
higher than room temperature even just before the irradiation with
the light 78. That is, the active alignment method can assist
melting the solder layer 58 (58') by the light 78.
The light 78 is preferably emitted to at least one of side surfaces
2303, 2304 and 2305 of the unit substrate 230 that are adjacent to
the joining surface 2300. This prevents the light 78 from hitting
the slider substrate 220 to heat the slider substrate 220 before
the light 78 reaches the solder layer 58 (58'). Furthermore, the
slider substrate 220 is preferably made of a material that has a
lower thermal conductivity than the material of the unit substrate
230. For example, if the unit substrate 230 is made of Si (thermal
conductivity: 168 W/(mK)), the slider substrate 220 is preferably
made of a material such as AlTiC (Al.sub.2O.sub.3--TiC) (thermal
conductivity: 19.0 W/(mK)) or SiO.sub.2 (thermal conductivity: 10.7
W/(mK)). In the slider 22, there is provided a magnetic head
element 32 including an MR element 33 and an electromagnetic
transducer 34. If these elements are heated to temperatures higher
than 200.degree. C., for example, by heat 79 from the solder layer
58 (58'), the MR multilayer 322 of the MR element 33 (FIG. 5) tends
to degrade, or the main magnetic pole 3400, the lower shield 3450
(FIG. 5) or the like of the electromagnetic transducer 34 tends to
thermally expand to protrude to an undesirable extent, which can
result in defects. However, if the conditions of irradiation
direction and thermal conductivity described above are satisfied,
excessive heating of the slider substrate 220 by irradiation with
the light 78 is avoided, and the amount of heat conducted to the
slider substrate 220 out of the amount of heat generated from the
solder layer 58 (58') and the unit substrate 230 can be reduced.
Consequently, adverse influence of heat on the MR element 33 and
the electromagnetic transducer 34 can be suppressed.
It is also preferable that heat generated from the solder layer 58
(58') and the unit substrate 230 by irradiation of the light 78 is
dissipated to the outside world through the holding jig 71 holding
the light source unit 23. The laser diode 40 provided in the light
source unit 23 usually does not degrade on exposure to a high
temperature on the order of 400.degree. C., for example. However,
in order to avoid excessive heating of the laser diode 40 and the
magnetic head element 32 described above, the holding jig 71 is
preferably made of a material such as a metal that has a high
thermal conductivity so that the holding jig 71 functions as a
heatsink during irradiation with light 78. It should be noted that
the heat dissipation by the holding jig 71 is adjusted so that the
solder layer 58 (58') sufficiently melts by the irradiation with
light 78 and the assistance of heat from the laser diode 40.
FIGS. 8a to 8c show perspective views schematically illustrating
another embodiment of the method for manufacturing the
thermally-assisted magnetic recording head 21 according to the
present invention, in which the light source unit 23 and the slider
22 are joined with each other.
Referring to FIG. 8a, first the active alignment method is used to
align the light source unit 23 and the slider 22 with each other as
described with reference to FIGS. 7a and 7b, to determine the
positions of the light source unit 23 and the slider 22 with a
solder layer 58 sandwiched between them. Then, as shown in FIG. 8b,
the solder layer 58 is irradiated with light 80 such as Nd-YAG
laser light through the unit substrate 230 to melt and solidify the
solder layer 58 to bond the light source unit 23 and the slider 22
together as described with reference to FIG. 7c.
Here, depending on the conditions of irradiation with the light 80
and the position and state of the solder layer 58, the solder layer
58 can be partially melted by the light 80, the rates of melting
can vary from location to location, or the rates of solidification
after the melting can differ from location to location. Such
variations can generate a force that moves the light source unit 23
and the slider 22. Further, depending on the degree of the force,
the light source unit 23 and the slider 22 which have been aligned
can be displaced with respect to each other after irradiation with
light 80.
In order to resolve such displacement, multiple Nd-YAG laser
oscillators 90, 91 and 92 are provided beforehand as illustrated in
FIG. 8c, and the radiation apertures of optical fibers 93, 94 and
95 are arranged in such a way that the solder layer 58 can be
irradiated with beams of light 80, 81 and 82 from different
directions. Then, the amount of displacement of the light source
unit 23 and the slider 22 with respect to each other is obtained
beforehand in the case that the solder layer 58 is irradiated with
a predetermined one shot (pulse) of each of the beams of light 80,
81 and 82. Then, the laser diode 40 is actually activated and laser
light 72 emitted from the light-emission center 4000 is monitored
in real time by a photodetector 74 provided on the head end surface
2210 side while the Nd-YAG laser oscillators 91, 91 and 92 are
activated as appropriate to irradiate the solder layer 58 with an
appropriate number of shots of each light beams 80, 81 and 82. In
the irradiation, the appropriate number of shots of each light
beams 80, 81 and 82 is made by taking into consideration the amount
of displacement caused by the predetermined one shot of each light
beam 80, 81 and 82, so that the maximum monitor output is provided
from the photodetector 74, thereby correcting the positions.
According to the method described above, alignment using the active
alignment method can be accomplished with high accuracy while
irradiating the solder layer 58 with light beams 80, 81 and 82 from
different directions to repeatedly melt the solder layer 58.
Consequently, variations in relative positions of the light source
unit 23 and the slider 22 caused by melting of the solder layer 58
can be corrected to ensure reliable bonding of the light source
unit 23 and the slider 22 in a desired position.
The method does not necessarily need multiple Nd-YAG laser
oscillators. For example, an optical switch may be provided so that
a single Nd-YAG laser oscillator 90 can provide laser light into
any of the optical fibers 93, 94 and 95. Alternatively, a set of
Nd-YAG laser oscillator 90 and optical fiber 93 may be moved as
appropriate to provide light beams 80, 81 and 82 from different
directions. Furthermore, the number of light beams from different
directions for melting the solder layer 58 is not limited to three;
two or more than three light beams may be used.
(Practical Examples of Joining)
Practical examples of joining between a light source unit 23 and a
slider 22 according to the present invention will be described
below.
In the practical examples, a light source unit 23 including a unit
substrate 230 made of Si (silicon) was joined to a slider 22
including a slider substrate 220 made of AlTiC
(Al.sub.2O.sub.3--TiC) by using circularly-polarized Nd-YAG laser
light 78 with a wavelength .lamda. of 1064 nm. A solder layer 58
was made of Sn (with a melting point of 231.degree. C.) or an AuSn
alloy (containing 80 weight % of Au and having a melting point in
the range of approximately 280 to 300.degree. C.) and provided in
the back surface 2201 of the slider substrate 220. A 5-nm-thick
foundation layer of Ta and a 100-nm-thick reflective layer 57 of Au
were provided in the joining surface 2300 of the unit substrate
230.
Output power of the Nd-YAG laser light 78 was 0.7 kW and the
irradiation time was 3, 4 or 5 msec (milliseconds). The spot
diameter of the laser light 78 was adjusted with an aperture to 50
.mu.m. Under these conditions, side surfaces 2303 and 2305 (FIG.
7c) of the unit substrate 230 are irradiated with the Nd-YAG laser
light 78. That is, the laser light 78 was applied from two
directions: the side surface 2303's side and the side surface
2305's side.
Shearing forces that are parallel to the back surface 2201
(YZ-plane) and parallel to each other but opposite in direction
were applied to the light source unit 23 and the slider 22 joined
together under the conditions described above to remove the light
source unit 23 from the slider 22. In doing so, the smallest
shearing force f.sub.S required for the removal was measured.
Table 1 gives the smallest shearing forces f.sub.S for samples that
had a solder layer 58 made of Sn or an AuSn alloy (containing 80
weight % of Au) and were joined under irradiation for 3, 4 or 5
msec.
TABLE-US-00001 TABLE 1 Irradiation time (msec) 3 4 5 Smallest
shearing Sn 200 260 220 force f.sub.s (gf) AuSn 30 250
Referring to Table 1, the smallest shearing forces f.sub.S for the
solder layers 58 made of Sn (with a melting point 231.degree. C.)
irradiated with Nd-YAG laser light 78 for 3, 4 and 5 msec are
greater than or equal to 200 grams-force (gf), which is
sufficiently large. Therefore it will be understood that a
sufficiently high strength of joining between the light source unit
23 and the slider 22 has been achieved by using the solder layer 58
made of Sn which has a melting point of less than or equal to
250.degree. C., which is sufficiently low. On the other hand, in
the case of the solder layer 58 made of an AuSn alloy (containing
80 weight % of Au and having a melting point in the range of
approximately 280 to 300.degree. C.) and irradiated with Nd-YAG
laser light 78 for 5 msec, the smallest shearing force f.sub.S is
greater than 200 gf, which is sufficiently large. However, in the
case of the solder layer 58 of the AuSn alloy irradiated for only 4
msec, the smallest shearing force f.sub.S is only 30 gf, which can
mean an insufficient joining force.
A longer irradiation time with the Nd-YAG laser light 78 can
adversely affect the joining between the unit substrate 230 and the
laser diode 40 with the solder layer 52. For example, if both of
the solder layers 52 and 58 are made of an AuSn alloy (containing
80 weight % of Au), the solder layer 52 will melt under the
influence of a temperature of the order of 280 to 300.degree. C. at
which the solder layer 58 melts. On the other hand, if the solder
layer 52 is made of an AuSn alloy (containing 80 weight % of Au)
and the solder layer 58 is made of Sn, the solder layer 52 does not
melt at 231.degree. C. at which the solder layer 58 melts.
Accordingly, good joining between the unit substrate 230 and the
laser diode 40 can be maintained. It will be understood from the
foregoing that it is more preferable that the solder layer 58 be
made of Sn, which has a lower melting point of 250.degree. C. or
lower.
(Effect of Polarization of Light 78)
If a reflective layer 57 is provided on the joining surface 2300 of
the unit substrate 230 as illustrated in FIGS. 3, 7a and 7c, most
of the light 78 incident on the unit substrate 230 and propagating
through the unit substrate 230 toward the joining surface 2300 is
reflected by the reflective layer 57, and therefore the solder
layer 58 is practically not directly heated. In practice, if the
unit substrate 230 is made of Si and the light 78 propagating
through the unit substrate 230 is Nd-YAG laser light, the energy of
the Nd-YAG laser light 78 is absorbed into the unit substrate 230
(Si) with a loss of approximately 5 dB/cm. Heat equivalent to the
absorbed energy increases the temperature of the unit substrate
230. As a result, the solder layer 58 is heated and melts. The
degree of absorption varies depending on the polarization of Nd-YAG
laser light 78 as well as the incident angle of the Nd-YAG laser
light 78 to the unit substrate 230. An example is given below in
which the effect of polarization of Nd-YAG laser light 78 on
absorption was studied in simulation.
FIG. 9 shows a schematic view illustrating an experimental system
used in the simulation for studying the effect of polarization of
Nd-YAG laser light 78 on absorption of the Nd-YAG laser light 78
into the unit substrate 230.
As shown in FIG. 9, a 5-nm-thick foundation layer 570 of Ta and a
100-nm-thick reflective layer 57 of Au were formed in sequence on
the joining surface 2300 of the unit substrate 230. A 5-nm-thick
foundation layer 570' of Ta, a 10-nm-thick adhesion layer 57' of
Au, and a 300-nm-thick solder layer 58 of Sn, which was a unit
adhesion material layer, were formed in sequence on the back
surface 2201 of the slider substrate 220. The unit substrate 230
was placed in contact with the slider substrate 220 in such a
manner that the surface of the reflective layer 57 and the surface
of the solder layer 58 are joined together.
It was assumed that the side surface 2305 of the unit substrate 230
in contact with the slider substrate 220 was irradiated with Nd-YAG
laser light 78 while the opposite side surface 2303 was irradiated
with Nd-YAG laser light 78' so that the laser lights 78 and 78'
entered the unit substrate 230 from two directions. In the
respective cases that the Nd-YAG laser light 78, which was one of
the irradiated laser lights, was S-polarized and was P-polarized,
the amount that was absorbed into the reflective layer 57, the
solder layer 58 and the surrounding metal layers and the amount
that was absorbed into the unit substrate 230 were calculated in
the Nd-YAG laser light 78 propagating through the unit substrate
230.
Here, it was assumed that the unit substrate 230 was made of Si.
The width W.sub.UN of the unit substrate 230 along Y-axis direction
(the track width direction) was 500 .mu.m. The Nd-YAG laser light
78 was incident on the side surface 2305 of the unit substrate 230
at an incident angle of 45.degree. (degrees) through air (with a
refractive index n=1). The incident position was at a distance of
d.sub.IN=100 .mu.m from the joining surface 2300 in X-axis
direction. The light path length (in Region 1) of the Nd-YAG laser
light 78 propagating through the unit substrate 230 to the joining
surface 2300 was 495 .mu.m, and the light path length (in Region 2)
of the Nd-YAG laser light 78 reflected by the joining surface 2300
(the reflective layer 57) was 16 .mu.m (the total light path length
was 511 .mu.m).
Based on 100 (%) of the amount P.sub.ALL of the Nd-YAG laser light
78 before entering the unit substrate 230, the amount P.sub.1 of
laser light 78 immediately after entering the unit substrate 230
and the amount Ab.sub.1 of laser light 78 absorbed into the unit
substrate 230 (in Region 1) until the laser light 78 reached the
joining surface 2300 (the reflective layer 57, the solder layer 58
and the surrounding metal layers) were calculated to obtain the
amount Ab.sub.m of laser light 78 absorbed in the reflective layer
57, the solder layer 58 and the surrounding metal layers. Here, the
reflectivity of the reflective layer 57 was 98%.
Furthermore, the amount P.sub.2 of Nd-YAG laser light 78
immediately after being reflected by the reflective layer 57, the
amount Ab.sub.2 of laser light 78 absorbed in the unit substrate
230 (in Region 2) until the laser light 78 reached the side surface
2030, and the amount P.sub.3 of laser light 78 radiated through the
side surface 2030 to the outside were calculated to obtain the
amount (Ab.sub.1+Ab.sub.2) of laser light 78 ultimately absorbed
into the unit substrate 230.
Table 2 lists the calculated amounts Ab.sub.m of Nd-YAG laser light
78 absorbed into the reflective layer 57, the solder layer 58 and
the surrounding metal layers and the calculated amounts
(Ab.sub.1+Ab.sub.2) of Nd-YAG laser light 78 absorbed into the unit
substrate 230. In the table, S-polarized Nd-YAG laser light 78 is a
light whose electric field oscillates perpendicularly to the
incident plane (XY-plane in FIG. 9) (in Z-axis direction) whereas
the P-polarized Nd-YAG laser light 78 is a light whose electric
field oscillates in the incident plane (XY-plane in FIG. 9).
TABLE-US-00002 TABLE 2 P.sub.ALL P.sub.1 Ab.sub.1 Ab.sub.m Light
S-polarized 100 56.7 3.1 1.1 amount (%) P-polarized 100 81.3 4.5
1.5 P.sub.2 Ab.sub.2 P.sub.3 Ab.sub.1 + Ab.sub.2 Light S-polarized
52.5 0.1 35.8 3.2 amount (%) P-polarized 75.2 0.1 52.5 4.6
Referring to Table 2, the amount Ab.sub.m of S-polarized Nd-YAG
laser light 78 absorbed into the reflective layer 57, the solder
layer 58 and the surrounding metal layers is 1.1% whereas the
amount Ab.sub.m of P-polarized Nd-YAG laser light 78 is 1.5%. That
is, the amount of P-polarized Nd-YAG laser light 78 absorbed in the
solder layer 58 is greater than that of the S-polarized Nd-YAG
laser light 78 by a factor of approximately 1.4. Further, the
amount (Ab.sub.1+Ab.sub.2) of S-polarized beam Nd-YAG laser light
78 absorbed into the unit substrate 230 is 3.2% whereas the amount
(Ab.sub.1+Ab.sub.2) of P-polarized Nd-YAG laser light 78 absorbed
in the unit substrate 230 is 4.6%. That is, the amount of
P-polarized Nd-YAG laser light 78 absorbed in the unit substrate
230 is greater than that of S-polarized Nd-YAG laser light 78 by a
factor of approximately 1.4.
In general, the reflectivity of a P-polarized light entering a
transparent material such as glass through air is lower than the
reflectivity of an S-polarized light. The results listed in Table 2
show that the P-polarized Nd-YAG laser light 78 is more absorbed
into the unit substrate 230 and the solder layer 58 and
consequently melts the solder layer 58 more efficiently than the
S-polarized Nd-YAG laser light 78. In this case, less output power
of laser light is required during joining and, in consequence, the
laser oscillator can be reduced in size and cost. Therefore a
P-polarized light is preferable as the light 78 used in joining the
light source unit 23 to the slider 22. In an actual manufacturing
process, the plane of polarization can become out of alignment
because of maladjustments or errors in jigs used for adjusting
polarization. Therefore, preferably circularly- or
elliptically-polarized light 78, which includes a sufficient amount
of P-component, is used.
According to the present invention, since the unit adhesion
material layer (solder layer or layers 58, 58') can be melted using
light such as YAG laser light in joining the light source unit 23
to the slider 22 as has been described above, high alignment
accuracy can be achieved while a joint that has a higher joining
strength and is less prone to deterioration with time can be
provided. Furthermore, the use of a unit adhesion material layer
made of Sn or an Sn alloy, a Pb alloy or a Bi alloy enables joining
that does not adversely affect the joining between the unit
substrate 230 and a light source such as the laser diode 40 by a
light-source adhesion material layer (solder layer 52). Since the
unit adhesion material layer (solder layer or layers 58, 58') is
melted by irradiation on the unit substrate 230 with light such as
YAG laser light, adverse influence of heat generated by the
irradiation on the magnetic head element 32 in the slider 22 can be
avoided.
All the foregoing embodiments are by way of example of the present
invention only and not intended to be limiting, and many widely
different alternations and modifications of the present invention
may be constructed without departing from the spirit and scope of
the present invention. Accordingly, the present invention is
limited only as defined in the following claims and equivalents
thereto.
* * * * *